The Washington Post-ABC News poll showed Obama, D-Ill., had the support of 33 percent of likely caucus-goers polled, with Clinton, D-N.Y., gaining the support of 29 percent and former Sen. John Edwards, D-N.C., trailing with 20 percent support.
The 4-percentage-point margin of error in the poll indicated the race is in a deadlock.
Obama edged Clinton over the question of electability but Clinton outpaced Obama and other contenders on the issue of overall experience and the commitment of supporters.
Clinton had the advantage in the key senior citizen demographic but Obama has a 3-to-1 advantage over Clinton in the support of college-educated caucus-goers polled.
The second tier candidates continued to falter in the Iowa race. New Mexico Gov. Bill Richardson had 8 percent support in the poll, Sen. Joe Biden of Delaware registered 4 percent and Sen. Chris Dodd of Connecticut gained the support of 1 percent of likely caucus-goers.
The Dec. 13-17 telephone poll surveyed 652 Iowa adults.
The Iowa caucuses are scheduled for Jan. 3.